1. Field of the Invention
The present invention relates to a transport system and a method for controlling the system, in particular to an automatic wafer storage system and a method for controlling the system.
2. Description of Related Art
In recent years, Automated Material Handling System (AMHS) is commonly used in the semi-conductor manufacturing factory. The Automated Material Handling System is for transporting wafers to a manufacturing tool for processing. But the number of manufacturing tools (i.e. equipments) may be limited. Therefore, when a wafer has been processed in an equipment, the Automated Material Handling System may first transport the wafer to a buffer station to be stored for a while. After the next equipment has processed the prior wafer, the Automated Material Handling System transport the wafer from the buffer station to the now available equipment for a next process.
Though the Automated Material Handling System is commonly utilized, it still has defects as follows:
1. If the buffer station is not disposed near the equipment, the transport tool of the Automated Material Handling System may waste a substantial amount of time to transport a wafer from the buffer station to the equipment.
2. The movement of the transport tool of the Automated Material Handling System is along one direction. Therefore, if the transport tool does not locate the equipment precisely, the transport tool needs to move around the entire track of the Automated Material Handling System so as to loop back again in order to relocate the equipment.
3. The buffer station is only for storing without other functions, so that wafers need to wait for the transport tool to come, which wastes a lot of time.
Therefore, it is necessary to design a transport system and a method of controlling the system so as to overcome the above-mentioned problems.